feat(rebuild): SignatureSet, SignatureSetArray and verifyMultipleAggregateSignatures

[matthewkeil]

This PR is related to #88 and covers the verifyMultipleAggregateSignatures

Inclusions

• Move TestWorker and runTest to functions.h and functions.cc
• SignatureSet
• SignatureSetArray
• verifyMultipleAggregateSignatures
• verifyMultipleAggregateSignaturesSync
• Unit tests

How to test

NOTE: to build and test copy the blst folder into rebuild/deps/blst. This will go away when we merge but for now node-gyp gets heartburn when building deps in folder above the binding.gyp file

Unit tests are provided and should have 100% coverage. If you see an edge that may not be covered please feel free to bring it up and I will add the test case

cd rebuild
yarn
yarn build
yarn test:unit

[CLAassistant]

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